From the huge report I read up about them - they don't work or at least the Ram Air part doesn't.
What does work and out of all the factories Kwak came out top is the box resonance adding the HP gain.
For Ramair to work you need a jet and that's why they have them.
I'll be running mine with trumpets that have tea strainers bonded onto them and a bit finer mesh than the one that's set into the intake snout.
The box will get new seals put onto it and all openings will have grommets and acrylic filling up the voids to get the max pressure into the unit.
If you've got some cash to spend - do it, otherwise concentrate on other better power gaining items like slotted cams
DS
